Currently, a magnetic disk device, which is regarded as one satisfying requirements such as large capacity and rapid data transfer, is widely used as an external storage device for a computer system.
In recent years, a disk array device has received attention as a device which further satisfies high reliability and low price in addition to the above requirements. The disk array device is obtained by arranging a plurality of compact disk devices into which data is distributed for storage therein respectively.
David A. Patterson et al. of the University of California at Berkeley released a paper in which a large amount of data was distributed to many physical disks, and a disk array device for realizing redundancy of data in the event of disk failure was evaluated with classification thereof from Level 1 to Level 5 (ACM SIGMOD Conference, Chicago, Jun. 1-3, 1988, P109 to P116). The levels 1 to 5 for classifying a disk array device proposed by David A. Patterson et al. are referred to as RAID (Redundant Arrays of Inexpensive Disks) 1 to 5.
All the disk array devices have redundant data therein. Accordingly, even if a disk device constituting an array can not be used because of some problem and data can not be read out therefrom, it is possible to recover disappeared data by using the redundant data and remaining data.
However, if any of the disk devices remains faulty, the redundancy of the disk array device is low although recovery of the data is possible with difficulty. For this reason, when a disk device constituting the array is faulty, the disk device is removed from the arrayed disk devices as quickly as possible and a normal disk device needs to be incorporated therein anew.
Accordingly, when a disk device is faulty, the faulty disk is replaced with another disk for maintenance. But a version number of the firmware recorded in the disk device used for maintenance may be different from that of the disk devices which are already operating in the disk array device.
As the arrayed disk devices are operated by logically correlating a plurality of disk devices to each other as described above, it is desirable that all operations be the same on the correlated disks. That is because usage of disk devices with different version numbers of the firmware may cause contradiction in control logic, which may in turn generate an operational error.